Fish tank.

                            Fish.

Fish, any of roughly species of invertebrate creatures (phylum Chordata) plant in the fresh and swab waters of the world. Living species range from the primitive jawless lampreys and hagfishes through the cartilaginous harpies, skates, and shafts to the abundant and different bony fishes. Utmost fish species are cold-thoroughbred; still, one species, the opah (Lampris guttatus), is warm-thoroughbred. 

 The term fish is applied to a variety of invertebrates of several evolutionary lines.  As members of the phylum Chordata, fish share certain features with other invertebrates. These features are gill gashes at some point in the life cycle, a notochord, or cadaverous supporting rod, a rearward concave whim-whams cord, and a tail. Living fishes represent some five classes, which are as distinct from one another as are the four classes of familiar air-breathing creatures — amphibians, reptiles, catcalls, and mammals. For illustration, the jawless fishes (Agnatha) have gills in sacks and warrant branch cinctures. Extant agnathans are the lampreys and the hagfishes. As the name implies, the configurations of fishes of the class Chondrichthyes (from chondr, “ cartilage,” and ichthyes, “ fish”) are made entirely of cartilage. Ultramodern fish of this class warrant a syncope bladder, and their scales and teeth are made up of the same placoid material. Harpies, skates, and shafts are exemplifications of cartilaginous fishes.  Exemplifications range from the bitsy seahorse to the 450-kg (-pound) blue marlin, from the flattened soles and flounders to the cubical puffers and ocean sunfishes. Unlike the scales of the cartilaginous fishes, those of bony fishes, when present, grow throughout life and are made up of thin lapping plates of bone. Bony fishes also have an operculum that covers the gill gashes. 

Study of fishes. 

 The study of fishes, the wisdom of ichthyology, is of broad significance. Fishes are of interest to humans for numerous reasons, the most important being their relationship with and dependence on the terrain. A more egregious reason for interest in fishes is their part as a moderate but important part of the world’s food force. This resource, formerly allowed unlimited, is now realized to be finite and in delicate balance with the natural, chemical, and physical factors of the submarine terrain. Overfishing, pollution, and revision of the terrain are the principal adversaries of proper fisheries operation, both in fresh waters and in the ocean. (For a detailed discussion of the technology and economics of fisheries, see marketable fishing.) Another practical reason for studying fishes is their use in complaint control. As bloodsuckers on mosquito naiads, they help check malaria and other mosquito- borne conditions. 

Laboratory creatures. 

Fishes are precious laboratory creatures in numerous aspects of medical and natural exploration. For illustration, the readiness of numerous fishes to acclimate to prison has allowed biologists to study geste, physiology, and indeed ecology under fairly natural conditions. Fishes have been especially important in the study of beast geste, where exploration on fishes has handed a broad base for the understanding of the more flexible geste of the advanced invertebrates. The zebra fish is used as a model in studies of gene expression.

 Millions of people keep live fishes in home fences for the simple pleasure of observing the beauty and geste of creatures else strange to them. Aquarium fishes give a particular challenge to numerous aquarists, allowing them to test their capability to keep a small section of the natural terrain in their homes. Sportfishing is another way of enjoying the natural terrain, also indulged in by millions of people every time. Interest in terrarium fishes and sportfishing supports multimillion- bone diligence throughout the world.